Aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid are used to produce a variety of polyester products, important examples of which are poly(ethylene terephthalate) and its copolymers. These aromatic dicarboxylic acids are synthesized by the catalyzed autoxidation of the corresponding dialkyl aromatic compounds which are obtained from fossil fuels (US 2006/0205977 A1). There is a growing interest in the use of renewable resources as feed stocks for the chemical industries mainly due to the progressive reduction of fossil reserves and their related environmental impacts.
Furan 2,5-dicarboxylic acid (“FDCA”) is a versatile intermediate considered as a promising closest biobased alternative to terephthalic acid and isophthalic acid. It is synthesized by the catalytic oxidation of 5-(hydroxymethyl)furfural (5-HMF) as shown in equation 1 below; or by the catalytic oxidation of 5-HMF esters (5-R(CO)OCH2-furfural where R=alkyl, cycloalkyl and aryl) as shown in equation 2 below; or by the catalytic oxidation of 5-HMF ethers (5-R′OCH2-furfural, where R′=alkyl, cycloalkyl and aryl) as shown in equation 3 below; or by the catalytic oxidation of 5-alkyl furfurals (5-R″-furfural, where R″=alkyl, cycloalkyl and aryl) as shown in equation 4 below; in each case using a Co/Mn/Br catalyst system. Mixed feedstocks of 5-HMF and 5-HMF esters, mixed feedstocks of 5-HMF and 5-HMF ethers, and mixed feedstocks of 5-HMF and 5-alkyl furfurals can also be used.

We have found that the above reactions work well. However a number of impurities are produced, particularly mono-carboxylic acid species such as 5-formyl furan-2-carboxylic acid (FFCA). These mono-carboxylic acids are not desirable since they terminate the chain growth of a polymer resulting in lower polymer viscosity. If colored bodies are present in the crude FDCA or remaining in the product FDCA, these colored bodies carry through to compounds or polymers using the FDCA as a reactive monomer to thereby color the compound or polymer. Therefore, it is necessary to purify the crude FDCA to remove the color bodies while minimizing the presence of FFCA in the product FDCA.
In process for the manufacture of terephthalic acid, one conventional method of purifying crude terephthalic acid (CTA) is to produce purified terephthalic acid (PTA) is by subjecting the CTA to a hydrogenation treatment, where 4-CBA (a chain terminator) is hydrogenated to para-toluic acid and color bodies are hydrogenated to colorless solid compounds. To accomplish purification by hydrogenation, solid CTA particles are typically dissolved in a solvent (e.g., water), and the resulting solution is subjected to liquid-phase hydrogenation in the presence of a hydrogenation catalyst. Although effective to reduce yellowness, purification of CTA by hydrogenation can be expensive because it is conducted under high reaction temperatures thereby consuming a large amount of energy and conducted under high hydrogen partial pressure thereby consuming a large amount of hydrogen.
Thus, there remains a need to effectively reduce the color bodies in crude FDCA without consuming large amount of energy or hydrogen in the process.